Tunnel ventilation is done by designing and operating a system of fans, shafts, ducts and control devices that moves air through the tunnel in a controlled way. The aim is to manage exhaust gases, dust, heat and smoke so that conditions remain safe for users and maintenance crews in both normal operation and emergencies. The exact arrangement depends on tunnel length, traffic type, gradient, surrounding environment and regulatory requirements.
The process begins with choosing a ventilation concept. Common methods include longitudinal, transverse and semi-transverse ventilation. In longitudinal ventilation, air flows mainly along the length of the tunnel, driven by jet fans mounted in the roof or by axial fans at portals or ventilation shafts. This is widely used in road tunnels and many mining access tunnels because it is relatively simple and cost-effective. In transverse and semi-transverse systems, fresh air is supplied and exhausted through ducts running along the tunnel, with vents at intervals to distribute or collect air.
Once the concept is selected, engineers calculate the required airflow and fan duties. They estimate pollutant generation from vehicles or equipment, expected traffic density, tunnel length and cross-section, and allowable gas and visibility limits. Using these inputs, they determine how much air must be moved and what pressure the fans must generate. This defines the size and number of axial or centrifugal tunnel fans, jet fans, ducts and shafts needed to achieve the design conditions.
To implement tunnel ventilation, designers create a network of airflow paths and control devices. Intake shafts, portals and air inlets bring fresh air into the system. Exhaust shafts, stacks and outlet portals discharge used air at controlled locations. Dampers, fire doors and ventilation doors are installed to direct airflow, isolate sections and switch between normal and emergency modes. Jet fans are placed at intervals in the tunnel to impart momentum to the air and support longitudinal flow.
Modern tunnel ventilation is operated using monitoring and automation. Gas sensors, visibility meters, temperature probes and airflow instruments continuously measure conditions in the tunnel. A central control system uses this information to adjust fan speeds, start or stop fans and open or close dampers. In normal operation, it keeps pollutants below limits while minimizing energy use. In a fire, it switches to pre-planned smoke control strategies, such as driving smoke in one direction to protect evacuation routes.
In mining tunnels and underground industrial facilities, tunnel ventilation is integrated into the broader underground ventilation network. It must coordinate with mine ventilation fans, shafts and raises so that both production areas and transport tunnels receive adequate airflow. Regular inspections, maintenance and ventilation surveys confirm that the system works as designed.
In summary, tunnel ventilation is done by combining a well-chosen ventilation concept with correctly sized fans, shafts, ducts, dampers and automated controls. Together, these elements move air along or across the tunnel to manage exhaust gases, dust, heat and smoke throughout the tunnel’s life.
